This disclosure relates to a vehicle headlamp system, and more particularly to a headlamp system that employs a compact high intensity discharge lamp having at least two different lighting functions or modes (e.g., “high beam” and “low beam” modes) integrated into a single headlamp assembly. Selected aspects of this disclosure may also find application in related headlamp arrangements.
Light collection efficiency of state of the art ellipsoidal projector modules of a projector-type automotive headlamp is moderate. Limitations associated with the light collection efficiency are basically driven by light absorption by the cut-off shield inserted into the module to block unwanted light rays when operated in “low beam” mode. The unwanted light rays in this mode are those that would otherwise be directed by the headlamp toward the eyes of an oncoming driver approaching the vehicle from the opposite direction. The cut-off shield defines a sharp light-to-dark cut-off in the headlamp beam. The cut-off line produced by the light blocking cut-off shield is preferably a straight, substantially horizontal line in the lanes of oncoming traffic. Further, the cut-off line is a skewed straight line in the lanes of the driver having the headlamp installed in his vehicle. In other words, beam cut-off is a means to avoid glare to oncoming drivers and partly to avoid glare for drivers moving in front of or close to the vehicle when in a “low beam” mode of the headlights. The beam cut-off also allows lighting of the road edge in the driving direction so that, for example, roadway signs are illuminated by the headlamp in the “low beam” mode.
Light collecting efficiency of a projector module can be increased by making an ellipsoidal projector module more compact and with a smaller opening area for the projector lens. Unfortunately, this proposed solution also has drawbacks. For example, the small surface area of the projector lens means higher surface brightness, which can cause discomfort glare to oncoming drivers. Accordingly, a diameter of the lens is thus preferably limited to be not less than approximately 60 millimeters minimum, since the glare can be uncomfortable or disturbing with lenses of diameters as low as less than 60 millimeters. Consequently, a new ellipsoidal projector module construction that eliminates, or at least reduces, light losses due to cut-off shield absorption and other loss mechanisms in the projector modules could have an advantageous impact in headlamp design technology.